Abstract

An immunohistochemical method was used to study the distribution and changes with time of the astrocytic reaction in the gerbil hippocampus following transient ischemia. Three markers were investigated with specific antibodies to glial fibrillary acidic protein (GFAP), glutamine synthetase (GS), and S-100 protein. On Day 2 after ischemia, and more prominently on Day 3, reactive astrocytes were intensely stained for GFAP in the hippocampal formation, especially in the CA1 region and dentate gyrus. This response by astrocytes preceded CA1 pyramidal cell degeneration, which became apparent on Day 5. On Day 5, immunoreactive cells were not stained as intensely as on Day 3, but cells in the CA1 region and dentate gyrus were still more intensely stained than those in normal animals. GS and S-100 showed similar changes in distribution after ischemia, although the change in GS was less prominent: the hilus of the dentate gyrus was most intensely stained. Both immunoreactivities seemed to increase rather transiently on Day 2 or 3 and to decrease to the initial level on Day 5. The fact that reactive astrocytes appeared in CA1 before the onset of visible neural degeneration indicates that signals from indisposed neurons may be transmitted to astrocytes for their quick functioning. It is also suggested that degenerative changes occur in the dentate gyrus and may be involved in the delayed neural death of CA1 pyramidal cells. These observations indicate that astrocytes play a role in the neural degeneration induced by ischemia and that several types of astrocytes seem to react differently.